The treatment of tumors generally involves operative resections, radiation therapy and chemotherapy, or else a combination of these methods. In the case of radiation therapy, the objective of the treatment is to apply a high, localized dose to the tumor with the least possible detrimental impact on the surrounding normal tissue. For this purpose, the energy or dose deposition of the radiation is adapted as closely as possible to the tumor. Recently, good therapeutic outcomes have been achieved with radiation with ions instead of photons since the energy or dose deposition has a sharp maximum (so-called Bragg peak) as a function of the penetration depth. In a generally known method, the beam is applied with passive beam formation components (among others, scatter films, modulators, collimators, compensators). As an alternative, however, it is also possible to focus the ion beam precisely and to scan the tumor three-dimensionally with a needle-fine beam, a so-called “pencil beam” (raster scan method, spot scan method, continuous scan method). In the raster scan method, the beam remains on one raster position for a defined number of particles and is kept switched on while it is changed to the next raster position. In the spot scan method, the beam is switched off between the raster positions, and with the continuous scan method, the beam is moved continuously at an optimized solenoid current sequence over the raster positions without stopping on them. Aside from protons, ions of the second period of the periodic table, especially carbon ions, are currently used. At times, neon ions are also employed. The use of these ions is characterized by a relative biological effectiveness (RBE) that is greater than that of photons and also of protons when it comes to the inactivation of cells. Due to their dependence on the dose level, on the type of tissue and, above all, on the particle type and particle energy, the relative biological effectiveness of the ions yields an additional therapeutic benefit in the area of the tumor.
In recent years, considerable clinical success has been achieved with radiation procedures using the raster scan method with carbon ions and dedicated radiation planning. The advantages of this method are the virtual elimination of absorber materials in order to avoid the generation of secondary particles and, above all, the good conformity of the generated dose distributions, especially proximally to the tumor.
Initially, such treatment was used mainly for tumors in the region of the base of the skull and along the spinal column whose motion can be reduced to a negligible minimum through stereotactic fixation. With the planned broader clinical application of the raster scan method in various therapy centers, however, other tumors are also going to be irradiated with carbon ion beams using the raster scan method. Tumors in the torso region of the body, however, are subject to more motion, especially due to the breathing or sometimes even due to the heartbeat of the patient, causing the entire rib cage to move and change shape. When moving tumors or, in general, moving target volumes are treated using the raster scan method, one is faced with the challenge that this motion can have a detrimental effect on the homogeneity of the energy deposition of the carbon ions in the tissue. Experiments with phantoms have shown that, when a beam is applied by means of scanning, overdoses and underdoses can occur in the target volume, so that a simple enlargement of the target volume by the magnitude of the motion, as is employed in the case of passive beam application, does not allow optimal treatment.
In order to correct the influence of the motion when a beam is applied by means of scanning, at the present time, irradiation making use of safety margins, multifold radiation, interrupted radiation, motion-compensated radiation or combinations of these cited methods is being studied and used in preclinical trials. During the motion-compensated irradiation, the beam position is continuously adapted to the motion of the tumor. Here, the beam position laterally to the beam direction, and, if applicable, the particle range are continuously adapted to the motion of the tumor. In this context, mention is made of the dissertations by S. O. Grötzinger, “Volume Conformal Irradiation of Moving Target Volumes with scanned ion beams,” Technical University of Darmstadt, Germany, 2004, and by C. Bert, “Bestrahlungsplan für bewegte Zielvolumina in der Tumortherapie mit gescanntem Kohlenstoffstrahl,” (Radiation plan for moving target volumes in tumor therapy with a scanned ion beam), Technical University of Darmstadt, Germany, 2006, both of which are hereby incorporated in their entirety by reference herein. In any case, the motion-compensated raster scan ion beam application is fundamentally known to the person skilled in the art working in the field of particle-beam tumor therapy.
The cited dissertations, however, deal mainly with the physical energy deposition of the ion beams and did not take the greater biological effectiveness into consideration.
German patent application DE 10 2007 045 879 of Siemens AG and of the applicant, which is hereby incorporated in its entirety by reference herein, describes a method and a device for the irradiation of moving target volumes.